HomeMy WebLinkAboutCT 12-05; La Costa Residential; Tentative Map (CT) (4)ITECHNICAL UPDATE AND ........... ,..",... .. ·o GEOTECHNICAL INVESTIGATION
PROPOSED LA COSTA TOWN CENTER
RESIDENTIAL DEVELOPMENT,
CARLSBAD, CALIFORNIA
Prepared for:
TAYLOR MORRISON OF CA, LLC
8105 Irvine Center Drive, Suite 1450
Irvine, California 92618
Project No. 042631-001
November 16, 2012
..._ __ Leighton and Associates, Inc. ---
A LEIGHTON GROUP COMPANY
Leighton and Associates, Inc.
A LElGHTON GROUP COMPANY
November 16, 2012
Project No. 042631-001
Taylor Morrison of CA, LLC
8105 Irvine Center Drive, Suite 1450
Irvine, California 92618
Attention:
Subject:
Ms. April Tornillo
Geotechnical Update and Addendum to Geotechnical Investigation
Proposed La Costa Town Center
Residential Development
Carlsbad, California
References: Leighton and Associates, Inc. 2012, Geotechnical Investigation, Proposed La
Costa Town Center Residential Development, Carlsbad, California, Project No.
042631-001, dated March 3, 2012
Latitude 33, 2012, Grading Plans, La Costa Town Center, Received October
2012
In accordance with your request and authorization, we have prepared this geotechnical update
and addendum letter for the proposed La Costa Town Center, Carlsbad, California. As part of this
update and addendum, we attended a project meeting on October 16, 2012, reviewed the above-
referenced geotechnical report along with recent project grading plans. As requested by Taylor
Morrison, the purpose of our update letter is revise geotechnical recommendations for building
pad over-excavation from 4 feet to 3 feet, and to update our geotechnical map and geologic
cross-section to new building pad elevations that have recently been raised.
Based on our review of the current grading plans for the project prepared by Latitude 33, (Latitude
33, 2012), we understand the proposed development will include construction of thirty-two single-
family residential buildings and associated improvements including roadways, building patios,
driveways, parking areas, concrete flatwork, underground utilities, landscaping, etc. We also
3934 Murphy Canyon Road, Suite 8205 • San Diego, CA 92123-4425
858.292.8030 • Fax 858.292.0771 • www.leightongroup.com
•
042631-001
understand that the proposed buildings will be two story structures and will likely be constructed
with conventional or post-tension foundations. Based on the preliminary development plans, we
anticipate the proposed finish grade elevations will be within a 1 to 5 feet of the existing mass-
graded pad elevations. In addition, the proposed building pad grades on recent grading plans
were raised approximately 1 foot.
Addendum Recommendations
In general, the geotechnical conditions of the site remain essentially as presented in the
referenced geotechnical report, and it is our professional opinion that our previous geotechnical
recommendations are still applicable and should be incorporated into the design, grading and
construction of the proposed development, including addendum recommendations provided
below. Note that we also recommend that the grading, retaining wall, and foundation plans be
reviewed by Leighton prior to commencing construction.
• Mitigation of Cut/Fill Transition Conditions and Building Pad Overexcavation
In order to reduce the potential for differential settlement in areas of transition or cut-fill
building pads and to remove metavolcanic rock in cut areas, we recommend that the
entire cut portion of the building pad be overexcavated to a minimum depth of 3 feet below
finished grade and replaced with properly compacted fill. This depth may be increased
depending on adjacent fill depth as part of the recommended removals of artificial fill
beneath the building pads. The overexcavation and recompaction should laterally extend
at least 5 feet beyond limits of the building footprint. Based on our review of the updated
grading plans, we have provided an approximate location of building pads
overexcavations (Plate 1 ). Note that Leighton previously recommended 4 foot pad
overexcavations was to mitigate risk of encountering difficult to non-rippable rock, minor
grade variations during grading and to facilitate foundation and utility trench excavations.
For deep utilities, we recommend the utility adjustments (streets, etc.) be over-excavated
a minimum of 1 foot below the deepest utility.
The recommendations provided in this update letter and our previous geotechnical report are
based on preliminary design information and subsurface conditions provided during previous
site As-graded reports. The interpolated subsurface conditions should be checked in the field
during grading and/or construction. Construction observation of all onsite excavations and field
density testing of all compacted fill should be performed by a representative of this office.
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If you have any questions regarding our update letter, please contact this office. We appreciate
this opportunity to be of service.
Respectfully submitted,
LEIGHTON AND ASSOCIATES, INC.
William D. Olson, RCE 45283
Associate Engineer
Mike D. Jensen, CEG 2457
Project Geologist
Attachment: Figures -Geotechnical Map and Geologic Cross-section
Appendix A-Geotechnical Report
Distribution: (6) Addressee
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~ICAL UPDATE INVESTIGATION,
tED LA COSTA TOWN CENTER
Kc~IDENTIAL DEVELOPMENT
CARLSBAD, CALIFORNIA
Prepared For:
TAYLOR MORRISON OF CA, LLC
8105 Irvine Center Drive, Suite 1450
Irvine, California 92618
Project No. 042631-001
September 27, 2012
._ ___ Leighton and Associates, Inc. ---
A LEIGHTON GROUP COMPANY
Leighton and Associates, Inc.
A LEIGHTON GROUP COMPANY
September 27, 2012
Taylor Morrison of CA, LLC
8105 Irvine Center Drive, Suite 1450
Irvine, California 92618
Attention:
Subject:
Ms. April Tornillo
Geotechnical Update Investigation
Proposed La Costa Town Center
Residential Development
Carlsbad, California
Project No. 042631-001
In accordance with your request and authorization, we have conducted a review of
pertinent documentation (SCS&T, 2012) and have prepared this geotechnical update
investigation for a proposed La Costa Town Center residential development to be built
north of Rancho Santa Fe Road, south of Old Rancho Santa Fe Road, and west of Paseo
Lupine in Carlsbad, California. Based on the results of our review, it is our professional
opinion that the site is suitable for the proposed residential development provided that
the recommendations presented herein are incorporated into the design, grading, and
construction of the site. The accompanying report presents a summary of our
investigation and provides preliminary geotechnical conclusions and recommendations
relative to the proposed site development. Note that additional site exploration is
recommended to further evaluate depth and characteristics of bedrock beneath the site.
If you have any questions regarding our report, please do not hesitate to contact this
office. We appreciate this opportunity to be of service.
Respectfully submitted,
Mike D. Jensen, CEG 245
Project Geologist
Distribution: (3) Addressee
William D. Olson, RCE 45283
Associate Engineer
3934 Murphy Canyon Road, Suite 8205 • San Diego, CA 92123-4425
858.292.8030 • Fax 858.292.0771 • www.leightongroup.com
042631-001
TABLE OF CONTENTS
Section
1.0 INTRODUCTION ...................................................................................................... 1
1.1 PURPOSE AND SCOPE .......................................................................................... 1
1.1.1 Scope ofWork ............................................................................................... 1
1.2 SITE LOCATION AND DESCRIPTION ........................................................................ 2
1.3 PREVIOUS SITE DEVELOPMENT AND SITE GRADING ................................................ 2
1.4 PROPOSED DEVELOPMENT ................................................................................... 3
1.5 PREVIOUS LABORATORY TESTING ......................................................................... 4
2.0 SUMMARY OF GEOTECHNICAL CONDITIONS .................................................... 5
2.1 GEOLOGIC SETTING ............................................................................................. 5
2.2 SITE-SPECIFIC GEOLOGY ..................................................................................... 5
2.2.1 Artificial Fill-Previously Existing (Afo) .......................................................... 5
2.2.2 Artificial Fill-Documented (Af) ..................................................................... 6
2.2.3 Santiago Peak Volcanics (Jsp) ...................................................................... 6
2.3 GEOLOGIC STRUCTURE ....................................................................................... 6
2.4 SURFACE AND GROUND WATER ........................................................................... 7
2.5 lANDSLIDES ........................................................................................................ 7
2.6 FLOOD HAZARD ................................................................................................... 7
2. 7 ENGINEERING CHARACTERISTICS OF THE ON-SITE SOILS ....................................... 7
2.7.1 Expansion Potential ....................................................................................... 7
2. 7.2 Earthwork Shrinkage and Bulking ................................................................. 8
2.7.3 Excavation Characteristics ............................................................................ 8
2.7.4 Oversize Material .......................................................................................... 9
3.0 FAULTING AND SEISMICITY ................................................................................ 10
3.1 FAULTING ......................................................................................................... 10
3.2 SEISMICITY ....................................................................................................... 1 0
3.2.1 Shallow Ground Rupture ............................................................................. 11
3.2.2 Liquefaction ................................................................................................. 11
3.2.3 Earthquake-Induced Settlement .................................................................. 11
3.2.4 Lateral Spread ............................................................................................. 11
3.2.5 Tsunamis and Seiches ................................................................................ 12
3.2.6 Building Code Seismic Parameters ............................................................. 12
4.0 CONCLUSIONS ..................................................................................................... 13
5.0 RECOMMENDATIONS .......................................................................................... 15
5.1 EARTHWORK ..................................................................................................... 15
5.1.1 Site Preparation ........................................................................................... 15
5.1.2 Excavations and Oversize Material ............................................................. 15
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TABLE OF CONTENTS (Continued)
Section
5.1.3 Fill Placement ..............•............................................................................... 16
5.1.4 Cut/Fill Transition Mitigation and Pad Overexcavation .........•...................... 17
5.2 ROCK FILL SPECIFICATIONS ..............••..............................•................................ 18
5.3 TEMPORARY EXCAVATIONS .........••..................................................................... 18
5.4 SURFACE DRAINAGE AND EROSION ........•...........................................•................ 19
5.5 FOUNDATION AND SLAB CONSIDERATIONS ........................................................... 19
5.5.1 Preliminary Foundation and Slab Design .................................................... 19
5.5.2 Settlement ..........•........................................................................................ 22
5.5.3 Post-Tension Foundation Recommendations .............................•................ 22
5.6 RETAINING WALL DESIGN AND LATERAL EARTH PRESSURE .................................• 24
5.7 PRELIMINARY PAVEMENT DESIGN ....................................................................... 25
5.8 SLOPE STABILITY ......................................................................•......................• 27
5.9 CONCRETE FLATWORK ••...................................•................................................ 27
5.10 SLOPE MAINTENANCE GUIDELINES ..................................................................... 27
5.11 LANDSCAPING AND POST-CONSTRUCTION ........................................................... 28
5.12 FUTURE INVESTIGATION ..................................................................................... 29
5.13 CONSTRUCTION OBSERVATION AND TESTING AND PLAN REVIEW ..........•................ 30
6.0 LIMITATIONS ......................................................................................................... 31
TABLES
TABLE 1 -EARTHWORK SHRINKAGE AND BULKING ESTIMATES-PAGE 7
TABLE 2-CBC SEISMIC DESIGN PARAMETERS-PAGE 11
TABLE 3-TEMPORARY EXCAVATION RECOMMENDATIONS-PAGE 17
TABLE 4-PRESOAKING RECOMMENDATIONS BASED ON
FINISH GRADE SOIL EXPANSION POTENTIAL-PAGE 20
TABLE 5-POST-TENSIONED FOUNDATION DESIGN RECOMMENDATIONS-PAGE 22
TABLE 6-STATIC EQUIVALENT FLUID WEIGHT (PCF)-PAGE 23
TABLE 7-PRELIMINARY PAVEMENT SECTION DESIGNS-PAGE-25
TABLE 8-PRELIMINARY CONCRETE PAVEMENT DESIGN-PAGE-26
FIGURE
FIGURE 1 -SITE LOCATION MAP -REAR OF TEXT
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TABLE OF CONTENTS (Continued)
Plate 1 -Geotechnical Map -In Pocket
Plate 2 -Geologic Cross Section -In Pocket
APPENDICES
APPENDIX A -REFERENCES
APPENDIX 8-LABORATORY TESTING AND DENSITY TESTING BY OTHERS
APPENDIX C-GENERAL EARTHWORK AND GRADING SPECIFICATIONS
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1.0 INTRODUCTION
1.1 Purpose and Scope
This report presents the results of our geotechnical update investigation for a
proposed residential development to be constructed on the existing sheet graded
parcel that is north of Rancho Santa Fe Road, south of Old Rancho Santa Fe
Road, and west of Paseo Lupino in Carlsbad, California, (see Figure 1 ).
Our investigation included a review of a previously Update Geotechnical
Investigation and the As-Graded Geotechnical reports (SCS&T, 2012), and
preparation of this report. The purpose of our geotechnical update investigation
was to evaluate existing geotechnical conditions present at the site and to
provide preliminary conclusions and geotechnical recommendations relative to
the proposed residential development of the property.
1.1.1 Scope of Work
As part of our geotechnical update, we performed the following:
• Review of available pertinent, published and unpublished geotechnical
literature maps, and aerial photographs (Appendix A).
• Review of the available previous geotechnical reports by others and
conceptual site development plans (SCS&T, 2012; Latitude 33, 2012).
• Field reconnaissance of the existing onsite geotechnical conditions.
• Review local and regional seismicity, and provide seismic parameters
for the site in accordance with 2010 California Building Code (CBC).
• An updated geotechnical map and geologic cross-section.
• Preparation of this report presenting our findings, conclusions, and
geotechnical recommendations with respect to the proposed design,
site grading and general construction considerations.
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1.2 Site Location and Description
The proposed project is located north of Rancho Santa Fe Road, southeast of Old
Rancho Santa Fe Road, and west of Paseo Lupine in Carlsbad, California. As
background this parcel, was previously mass-graded pad (SCS&T, 2012), and has
minor surface improvements consisting of a shallow concrete lined drainage
ditches, a desilting basin, and landscaping of perimeter slopes extending down Old
Rancho Santa Fe Road, Rancho Santa Fe Road, and along Paseo Lupine. The
topography of the area is gently sloping with elevations ranging from approximately
380 feet mean sea level (msl) in the north comer to approximately 380 feet msl in
the southeast corner and approximately 367 feet msl in the southwestern comer.
Vegetation at the site consists of native grasses and weeds. Descending 2:1 fill
slope, a fill over cut slope, a cut a slope all that borders the majority of the site
except along a segment along Old Rancho Santa Fe Road in the northeastern
section of the site.
Latitude: 33.0839 degrees
Longitude: -117.2339 degrees
1.3 Previous Site Development and Site Grading
As background, the site was rough graded in 2004 by Erreca's for Lusardi
Construction. The grading was observed and tested by Southern California Soil &
Testing (SCS&T, 2012). In general, grading consisted of installing keyways at the
toe of several fill slopes, creation of cut and fill slopes, installation of a subrain
trench backfill. Specifically, the grading consisted of excavating (i.e., cutting) the
eastern portion of the site and placement of fill in the western portion of the site.
Up to approximately 55 feet of fill was placed in the western portion of the site,
while cut excavations extended up to approximately 31 feet below the previous
existing grade at the eastern portion of the site. An overexcavation of the
previously proposed building pads and parking area cut portion was performed
into the underlying metavolcanic and replaced with capping fill material of less
than 6 inches in diameter. Previously proposed building pads were
overexcavated 2 to 7 feet below ground surface (bgs) and previously proposed
parking areas were overexcavated to a minimum of 10 feet bgs and replaced
with documented fill. Remedial grading consisted of removal of topsoil, alluvium,
and existing fill to depth up to 25 feet below previous existing grades. In the
southwest portion of the site, previous existing fills that were associated with
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grading and construction of Rancho Santa Fe Road were left-in-place. We have
provided a geotechnical map {Plate 1) with approximate remedial grading and
overexcavation elevations and limits of fill across the site.
Note that blasting of the underlying formational bedrock was required in the
eastern portion of the site. The resulting material, containing rock fragments of up
to 2 feet in diameter was then moisture conditioned and placed as fill.
Fills placed within the upper 5 feet of previously proposed building pads and the
upper 10 feet of previously proposed parking areas consisted of select capping
material, comprised primarily of silty sand and sandy silt with variable clay and
rock fragments generally no larger than 6 inches in diameter. Similar fill materials
were used as compacted fill within the outermost 6 feet of fill slopes. This select
capping material was derived from on-site non-organic topsoil and alluvial
deposits, and some borrowed material from off-site sources.
Excavations extending to metavolcanic rock were not scarified due to the nature
of the exposed material. Excavated soils, cuts, and imported fill were placed as
uniformly compacted fill material. The soils to be placed were moisture
conditioned and compacted to a minimum of 90 percent relative compaction.
1.4 Proposed Development
Based on our review of the conceptual site development plans (Latitude 33,
2012), we understand the proposed development will include construction of
thirty-two single-family residential buildings and associated improvements
including roadways, building patios, driveways, parking areas, concrete flatwork,
underground utilities, landscaping, etc. We also understand that the proposed
buildings will be two story structures and will likely be constructed with
conventional or post-tension foundations. Based on the preliminary development
plans, we anticipate the proposed finish grade elevations will be within a 1 to 4
feet of the existing mass-graded pad elevations.
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1.5 Previous Laboratory Testing
Laboratory testing was performed during the previous site grading to evaluate
maximum density and expansion index characteristics of the subsurface soils.
The previous laboratory tests performed by Southern California Soil & Testing
(SCS&T, 2012) are presented in Appendix B.
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2.0 SUMMARY OF GEOTECHNICAL CONDITIONS
2.1 Geologic Setting
The subject site is located in the coastal section of the Peninsular Range
Province, a geomorphic province with a long and active geologic history
throughout Southern California. Throughout the last 54 million years, the area
known as the "San Diego Embayment" has undergone several episodes of
marine inundation and subsequent marine regression, resulting in the deposition
of a thick sequence of marine and nonmarine sedimentary rocks on the
basement rock of the Southern California batholith.
Gradual emergence of the region from the sea occurred in Pleistocene time, and
numerous wave-cut platforms, most of which were covered by relatively thin
marine and nonmarine terrace deposits, formed as the sea receded from the
land. Accelerated fluvial erosion during periods of heavy rainfall, coupled with the
lowering of the base sea level during Quaternary time, resulted in the rolling hills,
mesas, and deeply incised canyons which characterize the landforms we see in
the general site area today.
2.2 Site-Specific Geology
Based on our review of the previous site geotechnical documents, a site
reconnaissance, and review of pertinent geologic literature and maps, the site is
generally underlain by documented artificial fill soils and the Jurassic-aged
Santiago Peak Volcanics. A brief description of the geologic units at the site are
presented below.
2.2 .1 Artificial Fill -Previously Existing (Afo)
Artificial fill placed during the previous grading operations along Rancho
Santa Fe Road. This fill is present below the fill slopes at the western end
of the site. As described, this fill generally consists of reddish-brown to
brown, medium dense to dense, moist, silty sands with clays, gravel, and
cobble. The estimated depth of fill beneath the existing slope faces should
be no greater than 10 feet below the adjacent roadway surface. These
artificial fills are expected to be suitable to support the proposed
residential development.
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2.2.2 Artificial Fill -Documented IAfl
Artificial fill placed during the previous site mass grading is anticipated to
be present throughout the entire site. The documented fill generally
consist of reddish-brown to brown, medium dense to dense, moist, silty
sands with clays, gravel, and cobble. The estimated depth of fill beneath
the existing site grades ranges from approximately 1.5 to 55 feet below
the existing surface grades. These artificial fills are expected to be suitable
to support the proposed residential development; although minor
reconditioning and/or removal of loose desiccated surficial soils may be
necessary. We have provided density tests and laboratory testing
(SCS&T, 2012) in Appendix B.
2.2.3 Santiago Peak Volcanics (Jsp)
Santiago Peak metavolcanic rock outcrops were observed across the
eastern portion of the site and underlie the entire site. The rock generally
consisted of light gray-olive brown to reddish brown, damp, highly
fractured, moderately to highly weathered metavolcanic rock. Where
observed, the metavolcanic rock becomes fresh bedrock is anticipated
within 2 feet to 10 feet of the surface. Excavations and cuts (greater than
±2 feet at the east end of the site will likely require very heavy ripping
and/or blasting and will likely generate some oversized materials. Fresh
rock zones may also be encountered at shallower depths. Additional
subsurface exploration is recommended to further evaluate depth bedrock
beneath the site.
2.3 Geologic Structure
Based on our review of the as-graded geotechnical report, and regional geologic
maps, the Jurassic-aged Santiago Peak Volcanics have a regional northwesterly
foliation/fracturing trend in the metavolcanic rock bedding and generally flat
bedding where present. Jointing was generally oriented parallel to previous
existing slopes with steep to moderate dip.
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2.4 Surface and Ground Water
No indication of surface water or evidence of surface ponding was encountered
during our review. However, surface water may drain as sheet flow in the higher
portions of the site during rainy periods and sheet across the lower portions of
the site.
Ground water was not reported during the original mass grading. Ground water
levels are anticipated to be relatively deep; however, perched ground water
conditions may develop following site development at contact areas of artificial fill
and the underlying bedrock. Ground water is not expected to impact the
proposed development.
2.5 Landslides
No ancient landslides were identified beneath or adjacent to the site. In addition,
no evidence of landsliding was documented during mass grading of the site. The
potential for significant landslides or large-scale slope instability at the site is
considered low.
2.6 Flood Hazard
According to a Federal Emergency Management Agency (FEMA) flood insurance
rate map (FEMA, 1997); the site is not located within a flood zone. Based on
review of dam inundation and topographic maps per SANGIS, the site is not
located downstream from dam inundation areas.
2.7 Engineering Characteristics ofthe On-Site Soils
Based on our review of previous site reports laboratory testing of representative
on-site soils and our professional experience on near-by sites with similar soils, the
engineering characteristics of the on-site soils are discussed below.
2.7.1 Expansion Potential
The majority of the onsite soils are expected to have a medium to high
expansion potential. The expansion index tests performed after site grading
ranged from 54 to 91 (SCS&T, 2012). Previous expansion index testing is
provided in Appendix B. Geotechnical observation and/or laboratory testing
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upon completion of the anticipated fine grading operations are
recommended to determine the actual expansion potential of finish grade
soils on the site.
2.7.2 Earthwork Shrinkage and Bulking
Based on our professional experience with similar projects in the general
vicinity of the site, we have estimated bulking and shrinkage of the on-site
soils. The volume change of excavated on-site materials upon
recompaction as fill is expected to vary with materials and location.
Typically, the surficial soils and bedrock materials vary significantly in
natural and compacted density, and therefore, accurate earthwork
shrinkage/bulking estimates cannot be determined. However, the following
factors (based on professional experience on nearby sites) are provided on
Table 1 as guideline estimates. If possible, we suggest an area where site
grades can be adjusted (during the later portion of the site grading
operations) be provided as a balance area.
Table 1
Earthwork Shrinkage and Bulking Estimates
Geologic Unit Estimated Shrinkage/Bulking
Documented and Existing Fills 0 to 3 percent shrinkage
Metavolcanic Rock (highly weathered) 0 to 10 percent bulking
Metavolcanic Rock (less-weathered) 5 to 15 percent bulking
2.7.3 Excavation Characteristics
It is anticipated the onsite fill soils can be excavated with conventional
heavy-duty construction equipment. However, excavations deeper than 5
feet, especially in the eastern portion of the site, is expected to be
marginally to nonippable in some area or will need to be blasted prior to
excavation.
Note that based on the current grading plans and review of the existing or
previously pad overexcavation limits, portions of the site will require
additional overexcavation of rock to depths of at least 4 feet below finish
grade. Note that the overexcavation will be within metavolcanic rock and
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may require heavy ripping or blasting. The approximate limits of
anticipated metavolcanic rock overexcavation is depicted on Geotechnical
Map (Plate 1 ). Also note that large rock may be generated during
overexcavation and the rock may have to be hauled off site or buried in
deep fill areas on the site. Additional subsurface exploration should be
performed to further characterize the bedrock.
2.7.4 Oversize Material
Numerous exposures of jointed metavolcanic bedrock occur across the site.
On average the jointed rock is anticipated to yield approximately one foot
diameter blocks with a potential for larger boulders. Based on our
professional experience with projects in similar geologic conditions, it is
likely that oversized rock will be generated during grading.
Recommendations have been provided for appropriate handling of
oversized materials.
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3.0 FAULTING AND SEISMICITY
3.1 Faulting
Our discussion of faults on the site is prefaced with a discussion of California
legislation and state policies concerning the classification and land-use criteria
associated with faults. By definition of the California Mining and Geology Board, an
active fault is a fault which has had surface displacement within Holocene time
(about the last 11,000 years). The state geologist has defined a potentially active
fault as any fault considered to have been active during Quaternary time (last
1,600,000 years). This definition is used in delineating Earthquake Fault Zones as
mandated by the Alquist-Priolo Earthquake Faulting Zones Act of 1972 and as
most recently revised in 2007 (Hart and Bryant, 2007). The intent of this act is to
assure that unwise urban development and certain habitable structures do not
occur across the traces of active faults. Based on our review, the site is not located
within any Earthquake Fault Zone (EFZ) as created by the Alquist-Priolo Act.
A review of available geologic literature pertaining to the subject site indicates that
there are no known active regional faults that transect the subject site. The nearest
known active regional fault is the Rose Canyon Fault Zone located approximately
7.1 miles west of the site.
3.2 Seismicity
The principal seismic considerations for most structures in southern California are
surface rupturing of fault traces and damage caused by strong ground shaking or
seismically induced ground settlement. Historically, the San Diego region has been
spared major destructive earthquakes. The site is considered to lie within a
seismically active region, as can all of Southern California.
The effect of seismic shaking may be mitigated by adhering to the California
Building Code (see Section 3.2.6 of this report for CBC seismic parameters) or
state-of-the-art seismic design parameters of the Structural Engineers
Association of California. Secondary effects associated with severe ground
shaking following a relatively large earthquake can include shallow ground
rupture, soil liquefaction, lateral spreading, earthquake-induced settlement, and
tsunamis/seiches. These secondary effects of seismic shaking are discussed in
the following sections.
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3.2.1 Shallow Ground Rupture
No active faults are mapped crossing the site. The nearest known active
fault is the Rose Canyon 7.1 miles west of the site. Due to absence of
known active faults, cracking due to shaking of a seismic event is not
considered a significant hazard, although it is possible at any site.
3.2.2 Liquefaction
Liquefaction and dynamic settlement of soils can be caused by strong
vibratory motion due to earthquakes. Both research and historical data
indicate that loose, saturated, granular soils are susceptible to liquefaction
and dynamic settlement. Liquefaction is typified by a total loss of shear
strength in the affected soil layer, thereby causing the soil to flow as a
liquid. This effect may be manifested by excessive settlements and sand
boils at the ground surface.
The unsaturated artificial fill and formational materials that underlie the site
are not considered liquefiable due to their dense physical characteristics
and lack of ground water.
3.2.3 Earthquake-Induced Settlement
Granular soils tend to density when subjected to shear strains induced by
ground shaking during earthquakes. Simplified methods were proposed by
Tokimatsu and Seed (1987) and Ishihara and Yoshimine (1992) involving
SPT N-values to estimate earthquake-induced soil settlement. However,
since liquefaction at the site is considered low, there is relatively no
potential for earthquake-induced settlements.
3.2.4 Lateral Spread
Empirical relationships have been derived by Youd and others (Youd,
1993; Bartlett and Youd, 1995; and Youd et. al., 1999) to estimate the
magnitude of lateral spread due to liquefaction. These relationships
include parameters such as earthquake magnitude, distance of the
earthquake from the site, slope height and angle, the thickness of
liquefiable soil, and gradation characteristics of the soil.
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Since there is relative no potential for liquefaction at the site, there is no
susceptibility to earthquake-induced lateral spread.
3.2.5 Tsunamis and Seiches
Based on the distance between the site and large, open bodies of water,
barriers between the site and the open ocean, and the elevation of the site
with respect to sea level, the possibility of seiches and/or tsunamis is
considered to be nil.
3.2.6 Building Code Seismic Parameters
The following geotechnical design parameters have been determined in
accordance with the 2010 CBC (CBSC, 2010) and the USGS Ground
Motion Parameter Calculator (Version 5.10).
Table 2
CBC Seismic Design Parameters
Description Values CBC Reference
Site Class D Table 1613.5.2
Short Period Spectral Acceleration s. 1.118 Figure 1613.5(3)
1-Second Period Spectral Acceleration s, 0.420 Figure 1613.5(4)
Short Period Site Coefficient Fa 1.053 Table 1613.5.3(1)
1-Second Period Site Coefficient Fv 1.58 Table 1613.5.3(2)
Adjusted Short Period Spectral SMs 1.177 Equation 16-36
Acceleration
Adjusted 1-Second Period Acceleration SM1 0.663 Equation 16-37
Design Short Period Spectral Sos 0.785 Equation 16-38
Response Parameter
Design 1-Second Period Spectral So, 0.442 Equation 16-39
Response Parameter
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4.0 CONCLUSIONS
Based on our review of the previously documented Update Geotechnical Investigation
and As-Graded Geotechnical reports (SCS&T, 2012), it is our professional opinion that
the proposed development of the site is feasible from a geotechnical standpoint,
provided the following conclusions and recommendations are incorporated into the
design, grading, and construction of the project. Additional subsurface exploration
should be performed to further characterize the bedrock beneath the site. The following
is a summary of the geotechnical factors that may affect development of the site.
• Based on our reference review, the documented fill and underlying formational
material are dense and well compacted, excluding the upper 1 to 2 feet which
appears dry and is disturbed and/or weathered. The upper 2 feet of existing fill is
considered unsuitable for support of additional fill soils, structural loads or surface
improvements in their present condition. Remedial grading measures such as
removals, scarification and recompaction will be necessary to mitigate this condition,
if not removed by the proposed grading.
• Based on the review of the as-graded documents, minimum fill depths across mass-
graded pad below the existing ground surface are on the order of approximately
2 feet beneath the proposed building footprints. Because site grades are being
lowered a cut/fill transition will be created and additional overexcavation will be
required. The pad overexcavations will encounter metavolcanic rock with oversized
rock material.
• Based on previous laboratory testing, the near surface soils on the site generally
possess a medium to high expansion potential. Measures to mitigate
expansive/swelling soils will be necessary during design and construction. Additional
expansion testing should be performed after pad grading is performed.
• Laboratory tests should be conducted to determine the onsite soils' potential for
sulfate exposure on concrete once pad grading is performed.
• The existing onsite soils appear to be suitable material for use as fill provided they
are relatively free of organic material, debris, and rock fragments larger than 8
inches in maximum dimension. Review of the as-graded report indicates that some
oversized material was generated during site grading but placed below proposed
foundation grades. However, in areas where proposed pad grades are lowered and
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deep utility excavations are planned, especially outside the previous pad
overexcavations (building and parking lot), oversized metavolanic rock should be
anticipated. Oversize material if encountered should be placed in nonstructural
areas or disposed of offsite.
• Ground water or seepage was not encountered during the previous site grading or
investigations (SCS&T, 2012); however, perched ground water and seepage may
develop during periods of precipitation.
• The site is located in an area underlain by the fill and formational material that is
known to contain both permeable and impermeable layers which can transmit and
perched ground water in unpredictable ways. Therefore, given the site geologic
conditions, the use of some LID measures may not be appropriate for this project.
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5.0 RECOMMENDATIONS
5.1 Earthwork
We anticipate that earthwork at the site will consist of site preparation, remedial
grading and placement of compacted fill. We recommend that earthwork on the
site be performed in accordance with the following recommendations and the
General Earthwork and Grading Specifications for Rough Grading included in
Appendix C. In case of conflict, the following recommendations shall supersede
those in Appendix C.
5.1 .1 Site Preparation
Prior to grading of areas to receive structural fill or engineered structures
and improvements, the areas should be cleared of surface vegetation, any
existing debris, and removal of potentially compressible material, which
includes the existing upper 1 to 2 feet of disturbed/weathered fill.
Vegetation and debris should be removed and properly disposed of offsite.
Holes resulting from the removal of buried obstructions, which extend below
finished site grades, should be replaced with suitable compacted fill
material. Areas to receive fill and/or other surface improvements should be
scarified to a minimum depth 8 inches, brought to above-optimum moisture
condition, and recompacted to at least 90 percent relative compaction
(based on American Standard of Testing and Materials [ASTM] Test
Method D1557). A Leighton representative should observe conditions
exposed in the bottom of the excavation to determine if additional removal
is required.
5.1.2 Excavations and Oversize Material
Based on the review of previous site reports and our site reconnaissance,
it appears that the near surface fill is rippable with heavy-duty construction
equipment in good working order (i.e. a single shank D9 Dozer or
equivalent). However, moderately difficult ripping to very difficult ripping
and localized blasting should be anticipated where Santiago Peak
Volcanic Rock is mapped near the surface, in the fill areas between 2 to 5
feet below the ground surface on the central and eastern portions of the
site, and where proposed pad grades are lower than existing grade.
Deeper excavations into the rock is expected to be marginally rippable to
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unrippable, becoming progressively less fractured with increasing depth.
Heavy/very difficult to unrippable and blasting is anticipated for planned
excavations below a depth of 2 feet and for localized areas within 10 feet
on the ground surface. Note previous cut-graded portions of the site will
likely encounter heavy/very difficult to unrippable rock significantly
shallower than anticipated. Localized residual boulders of dense rock are
also anticipated within otherwise rippable zones. The depth of mass-
graded pad overexcavation to metavolcanic rock and at grade
metavolcanic rock is displayed on the Geotechnical Map (Plate 1 }.
We understand that a portion of the site was overexcavated at the
previous proposed building pads and parking lot area, and were generally
capped with material not exceeding 6 inches in diameter. Outside the
limits of the previously overexcavated parking lot and proposed building
pads significant amount of rock including oversize material (i.e. rock
typically over 8 inches in maximum dimension} will be generated during
the grading of the site. Rocks greater than 8 inches in diameter should not
be placed within fill the upper three of fill. Note that the western portion of
the site (i.e. outside the limits of the previously proposed pads and parking
lot overexcavation} it is unknown if the fills near pad grade was capped
with material less 6 inches in diameter. Excavations in western portion of
the site should anticipate oversized rock material. All oversized rock that is
encountered should be placed as fill in accordance with the
recommendations in section 5.2 or hauled off site for disposal.
5.1.3 Fill Placement
The onsite soils are generally suitable for reuse as compacted fill, provided
they are free of organic materials and debris. Areas to receive structural fill
and/or other surface improvements should be scarified to a minimum depth
of 8 inches; brought to at least 3 percent above optimum moisture content;
and recompacted to at least 90 percent relative compaction (based on
ASTM Test Method 01557}. The optimum lift thickness to produce a
uniformly compacted fill will depend on the type and size of compaction
equipment used. In general, fill should be placed in uniform lifts not
exceeding 8 inches in thickness. Placement and compaction of fill should
be performed in general accordance with the current City of Carlsbad
grading ordinances under the observation and testing of the geotechnical
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consultant, sound construction practices, and the General Earthwork and
Grading Specifications for Rough Grading presented in Appendix C.
Proposed fills placed on slopes steeper than 5 to 1 {horizontal to vertical)
and repairs of the existing fill slopes should be keyed and benched into
dense formational or competent fill soils (see Appendix C for benching
details). Fills placed within 5 feet of finish pad grades should consist of
granular soils of very low to medium expansion potential and contain no
materials over 8 inches in maximum dimension. Oversize material, if
encountered, may be incorporated into structural fills if placed in
accordance with the recommendation of Appendix C.
Import soils, if necessary, should consist of granular soils of very low to low
expansion potential (expansion index 50) and contain no materials over 8
inches in maximum dimension.
5.1.4 Cut/Fill Transition Mitigation and Pad Overexcavation
In order to reduce the potential for differential settlement in areas of
transition or cut-fill building pads and to remove metavolcanic rock in cut
areas, we recommend that the entire cut portion of the building pad be
overexcavated to a minimum depth of 4 feet below finished grade and
replaced with properly compacted fill. This depth may be increased
depending on adjacent fill depth as part of the recommended removals of
artificial fill beneath the building pads. The overexcavation and
recompaction should laterally extend at least 5 feet beyond limits of the
building footprint. Based on our review of the preliminary plans, we provided
an approximate location of building pads overexcavations (Plate 1 ).
In order to reduce the potential for excessive differential settlement under
future building or retaining walls, the transition from cut to fill subgrade
should be gradual. We recommend that the maximum differential fill height
to not exceed 10 feet over a horizontal distance of 30 feet. The actual
overexcavation limits and depth should be further evaluated prior to the
grading operations based on the final design of the project and the actual
building location and dimension. Also, additional over-excavation or
deeper removals may be recommended during site grading based on the
actual field conditions.
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5.2 Rock Fill Specifications
We anticipate that the relatively shallow cuts on the mass graded pad that will
generate oversized rock. Fill placement 1 foot below deepest utilities in roadways
and within the upper 3 feet of finish grade, fill soils should not contain rock
greater than 8 inches in maximum dimension in order to facilitate foundation and
utility trench excavation. For fill soils between 3 and 10 feet below finish grade,
the fill may contain rock up to 12 inches in maximum dimension and should be
mixed with sufficient soil to eliminate voids. Below a depth of 10 feet and at least
3 feet horizontally from the slope face, rocks up to a maximum dimension of
36 inches may be incorporated into the fill utilizing rock blankets. A typical soil-
rock fill detail is included within Appendix C. Rocks up to 5 feet in maximum
dimension should be hauled offsite or utilized in nonstructural fill or landscaped
area.
5.3 Temporary Excavations
Sloped excavations may be utilized when adequate space allows. Based on
findings, we provide the following recommendations for sloped excavations in fill
soils or competent bedrock materials without seepage conditions.
Table 3
Temporary Excavation Recommendations
Excavation Maximum Slope Ratio Depth Below Maximum Slope Ratio
Adjacent Surface In Fill Soils In Competent Bedrock
(feet) Material
o to 5 %:1 (H: V) Vertical
5 to 20 1:1 1/2:1
Excavations greater than 20 feet in height will require an alternative sloping plan
or shoring plan prepared by a California registered civil engineer. The above
values are based on the assumption that no surcharge loading or equipment will
be placed within 10 feet of the top of slope. All excavations should comply with
OSHA requirements The contractor's "competent person" should review all
excavations on a daily basis for signs of instability.
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5.4 Surface Drainage and Erosion
Surface drainage should be controlled at all times. Proposed structures should
have an appropriate drainage system to collect roof runoff. Positive surface
drainage should be provided to direct surface water away from structures toward
the street or suitable drainage facilities. Planters should be designed with
provisions for drainage to the storm drain. Ponding of water should be avoided
adjacent to any structures.
Regarding Low Impact Development (LID) measures, we are of the opinion that
bioswales, infiltration basins, and other on site retention and infiltration systems can
potentially create adverse perched ground water conditions both on-site and off-
site. In particular, this site is underlain by fill or formations that are known to
contain both permeable and impermeable layers which can transmit and perch
ground water in unpredictable ways. Therefore, given the site geologic conditions
and project type, some types of LID measures may not be appropriate for this site
and project. We recommend that infiltration systems are lined with a 15 mil HOPE
impermeable liner.
5.5 Foundation and Slab Considerations
Foundations and slabs should be designed in accordance with structural
considerations and the following recommendations. These recommendations
assume that the soils encountered within 5 feet of pad grade have a medium to
high expansion potential (i.e. an expansion index less than 130) for expansion
and a differential fill thickness of less than 15 feet. Additional expansion testing
should be performed as part of the fine grading operations. If very high expansive
soils are encountered and selective grading cannot be accomplished, additional
foundation design may be necessary.
5.5.1 Preliminary Foundation and Slab Design
The proposed buildings may be supported by conventional, continuous or
isolated spread footings. Footings should extend a minimum of 30 inches
beneath the lowest adjacent soil grade. At these depths, footings may be
designed for a maximum allowable bearing pressure of 2,500 pounds per
square foot (psf) if founded in dense compacted fill soils. The allowable
bearing pressures may also be increased by one-third when considering
loads of short duration such as wind or seismic forces. The minimum
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recommended width of footings is 18 inches for continuous footings and
24 inches for square or round footings. Footings should be designed in
accordance with the structural engineer's requirements.
We recommend a minimum horizontal setback distance from the face of
slopes for all structural footings and settlement-sensitive structures. This
distance is measured from the outside edge of the footing, horizontally to
the slope face (or to the face of a retaining wall) and should be a minimum
of H/2, where H is the slope height (in feet). The setback should not be
less than 1 0 feet and need not be greater than 20 feet. Please note that
the soils within the structural setback area, other than those addressed
within this report, possess poor lateral stability, and improvements (such
as retaining walls, sidewalks, fences, pavements, etc.) constructed within
this setback area may be subject to lateral movement and/or differential
settlement.
Slabs on grade should be reinforced with reinforcing bars placed at slab
mid-height. Slabs should have crack joints at spacings designed by the
structural engineer. Columns, if any, should be structurally isolated from
slabs. Slabs should be a minimum of 5 inches thick and reinforced with
No. 4 rebars at 18 inches on center on center (each way). If applicable,
slabs should also be designed for the anticipated traffic loading using a
modulus of subgrade reaction of 100 pounds per cubic inch. All
waterproofing measures should be designed by the project architect.
In accordance with the current guidelines of the 2010 CALGreen Code,
Section 4.505.2, post-tensioned and conventional slabs should be underlain
by a vapor barrier which is in tum underlain by 4 inches of 1/2 inch gravel.
The slab subgrade soils should be presoaked prior to the placement of
gravel. ACI 302.2R-06 guidance recommends use of a vapor barrier with a
perm rating of 0.01 or less where moisture-sensitive floor coverings are
provided. The vapor barrier should possess adequate puncture resistance
such that these properties are preserved when subjected to construction
traffic.
Placement of concrete in direct contact with the vapor barrier requires
additional design and construction considerations on the part of the
structural engineer, architect and contractor. Additional guidance is
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provided in ACI Publications 302.1 R-04 Guide for Concrete Floor and Slab
Construction and 302.2R-06 Guide for Concrete Slabs that Receive
Moisture-Sensitive Floor Materials. Only an experienced concrete
contractor familiar with proper construction techniques needed for
constructing slabs directly on the vapor retarder/barrier should perform the
work.
The slab subgrade soils underlying the foundation systems should be
presoaked in accordance with the recommendations presented in Table 4
prior to placement of the moisture barrier and slab concrete. The subgrade
soil moisture content should be checked by a representative of Leighton
prior to slab construction.
Presoaking or moisture conditioning may be achieved in a number of ways.
But based on our professional experience, we have found that minimizing
the moisture loss on pads that has been completed (by periodic wetting to
keep the upper portion of the pad from drying out) and/or berming the lot
and flooding for a short period of time (days to a few weeks) are some of
the more efficient ways to meet the presoaking recommendations. If
flooding is performed, a couple of days to let the upper portion of the pad
dry out and form a crust so equipment can be utilized should be anticipated.
Table4
Presoaking Recommendations Based on Finish Grade Soil Expansion
Potential
Expansion Potential Presoaking Recommendations
Very Low Near-optimum moisture content to a minimum depth
of6inches
Low 120 percent of the optimum moisture content to a
minimum depth of 12 inches below slab subgrade
Medium 130 percent of the optimum moisture content to a
minimum depth of 24 inches below slab subgrade
High 130 percent of the optimum moisture content to a
minimum depth of 30 inches below slab subgrade
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5.5.2 Settlement
Fill depths between 2 and 55 feet are anticipated beneath the proposed
building footings following final grading. Based on this configuration, the
maximum total settiement is estimated at approximately 1 inch with
differential settlement anticipated to be approximately % to 1 inch over a
horizontal distance of 1 00 feet.
5.5.3 Post-Tension Foundation Recommendations
As an alternative to the conventional foundations for the buildings, post-
tensioned foundations may be used. We recommend that post-tensioned
foundations be designed using the geotechnical parameters presented in
table below and criteria of the 2010 California Building Code and the Third
Edition of Post-Tension Institute Manual. A post-tensioned foundation
system designed and constructed in accordance with these
recommendations is expected to be structurally adequate for the support of
the buildings planned at the site provided our recommendations for surface
drainage and landscaping are carried out and maintained through the
design life of the project. Based on an evaluation of the depths of fill
beneath the building pads, the attached Table 5 presents the
recommended post-tension foundation category for residential buildings on
subject site.
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Table 5
Post-Tensioned Foundation Design Recommendations
Category I Category II Category Ill
Very Low to Low Medium Expansion High Expansion
Expansion Potential Potential Potential
Design Criteria (EI 0 to 50) (EI 51 to 90) (EI91 to 130)
Differential Fill Differential Fill Differential Fill
Thickness less Thickness between Thickness between
than 10 feet 1 0 and 20 feet 20 and 40 feet
Edge Moisture Center Lift: 9.0 feet 8.3 feet 7.0 feet
Variation, em Edge Lift: 4.8 feet 4.2 feet 3.7 feet
Differential Swell, Center Lift: 0.46 inches 0.75 inches 1.09 inches
Ym Edge Lift: 0.65 inches 1.09 inches 1.65 inches
Perimeter Footing Depth: 18 inches 24 inches 30inches
Allowable Bearing Capacity 2,000 psf
The post-tensioned (PT) foundation and slab should also be designed in
accordance with structural considerations. For a ribbed PT foundation, the
concrete slabs section should be at least 5 inches thick. Continuous footings (ribs
or thickened edges) with a minimum width of 12 inches and a minimum depth of
12 inches below lowest adjacent soil grade may be designed for a maximum
allowable bearing pressure of 2,000 pounds per square foot. For a uniform
thickness "mat" PT foundation, the perimeter cut off wall should be at least 8
inches below the lowest adjacent grade. However, note that where a foundation
footing or perimeter cut off wall is within 3 feet (horizontally) of adjacent drainage
swales, the adjacent footing should be embedded a minimum depth of 12 inches
below the swale flow line. The allowable bearing capacity may be increased by
one-third for short-term loading. The slab subgrade soils should be presoaked in
accordance with the recommendation presented in Table 4 above prior to
placement of the moisture barrier.
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The slab should be underlain by a moisture barrier as discussed in Section 5.51
above. Note that moisture barriers can retard, but not eliminate moisture vapor
movement from the underlying soils up through the slabs. We recommend that the
floor covering installer test the moisture vapor flux rate prior to attempting
applications of the flooring. "Breathable" floor coverings should be considered if
the vapor flux rates are high. A slip-sheet or equivalent should be utilized above
the concrete slab if crack-sensitive floor coverings (such as ceramic tiles, etc.) are
to be placed directly on the concrete slab. Additional guidance is provided in ACI
Publications 302.1 R-04 Guide for Concrete Floor and Slab Construction and
302.2R-06 Guide for Concrete Slabs that Receive Moisture-Sensitive Floor
Materials.
Based on an overall geotechnical evaluation of the El values and their locations,
we anticipate Post-Tension Foundation Category II and Ill for the site.
5.6 Retaining Wall Design and Lateral Earth Pressure
We anticipate that several relatively small retaining walls are proposed at the
site. For design purposes, the following lateral earth pressure values for level or
sloping backfill are recommended for retaining walls backfilled with on site soils of
medium to high expansion potential (expansion potential greater than 50 per
ASTM Test Method 04829).
Table 6
Static Equivalent Fluid Weight (pcf)
Conditions Level 2:1 Slope
Active 40 65
At-Rest 55 90
300 140 Passive (Maximum of 3 ksf) (Sloping Down)
Unrestrained (yielding) cantilever walls up to 15 feet in height should be designed
for an active equivalent pressure value provided in table above. For the design of
walls restrained from movement at the top (nonyielding) such as basement walls,
the at-rest pressures should be used. If conditions other than those covered
herein are anticipated, the equivalent fluid pressure values should be provided on
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an individual case basis by the geotechnical engineer. A surcharge load for a
restrained or unrestrained wall resulting from automobile traffic may be assumed
to be equivalent to a uniform horizontal pressure of 75 psf which is in addition to
the equivalent fluid pressure given above. For other uniform surcharge loads, a
uniform horizontal pressure equal to 0.35q should be applied to the wall (where q
is the surcharge pressure in psf). To account for potential redistribution of forces
during a seismic event, basement walls, if any, that fall within the requirements of
ASCE 7-05 Section 15.6.1 should also be checked considering an additional
uniform seismic pressure distribution equal to 10H psf, where H equals the
overall retained height in feet. The wall pressures assume walls are backfilled
with free draining materials and water is not allowed to accumulate behind walls.
A typical wall drainage design is provided in Appendix D. Importing or selective
grading may be necessary to obtain retaining wall backfill material.
Wall backfill should be brought to at least 3 percent above the optimum moisture
content and compacted by mechanical methods to at least 90 percent relative
compaction (based on ASTM 01557). Wall footings should be designed in
accordance with the foundation design recommendations and reinforced in
accordance with structural considerations. The bearing pressure for retaining
walls should be limited to 2,500 psf for footing founded in compacted fill. Footing
embedment depth should be at least 18 inches below the lowest adjacent grade.
For all retaining walls, we recommend a minimum horizontal distance from the
outside base of the footing to daylight of 10 feet.
Lateral soil resistance developed against lateral structural movement can be
obtained from the passive pressure value provided above. Further, for sliding
resistance, the friction coefficient of 0.33 may be used at the concrete and soil
interface. These values may be increased by one-third when considering loads of
short duration including wind or seismic loads. The total resistance may be taken
as the sum of the frictional and passive resistance provided that the passive
portion does not exceed two-thirds of the total resistance.
5.7 Preliminary Pavement Design
The appropriate pavement section will depend on the type of subgrade soil, shear
strength, traffic load, and planned pavement life. Since an evaluation of the actual
subgrade soils cannot be made at this time, we have used an assumed R-value of
15 and Traffic Indices (TI) of 4.5, 5 and 6 for the parking/auto driveways and truck
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driveways, respectively. The range of onsite pavement sections presented on
Table 7 is to be used for preliminary planning purposes only. Final pavement
designs should be completed after R-value tests have been performed on actual
subgrade materials.
Table 7
Preliminary Pavement Section Designs
Traffic Index Preliminary Pavement Section
4.5 4 inches AC over 5 inches Class 2 Aggregate Base
5 4 inches AC over 6 inches Class 2 Aggregate Base
6 4 inches AC over 12 inches Class 2 Aggregate Base
Prior to placing the pavement section, the subgrade soils should have a relative
compaction of at least 95 percent to a minimum depth of 12 inches (based on
ASTM Test Method 01557). Aggregate Base should be compacted to a minimum
of 95 percent relative compaction (based on ASTM Test Method 01557) prior to
placement of the AC. All concrete pavement sections, including concrete curbs
and gutters, should be underlain by at least 6 inches of aggregate base (AB)
compacted to 95 percent relative compaction.
The Asphalt Concrete (AC) and Class 2 Aggregate Base shall conform to and be
placed in accordance with the latest revision of the California Department of
Transportation Standard Specifications (Section 26), the Greenbook specifications,
and/or the City of Carlsbad requirements. Asphalt Concrete shall conform to and
be placed in accordance with the "Greenbook" Standard Specifications for Public
Works Construction and the City of Carlsbad requirements.
The following table presents recommendations for the concrete pavement sections
subject to vehicle loading. Subgrade soils are assumed to have an R-value of least
15 and compacted to at least 95 percent relative compaction.
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Table 8
Preliminary Concrete Pavement Design
Traffic Index Minimum PCC Section
(MR = 600 psi min.)
5 6.5 inches PCC
6 7.0 inches PCC
5.8 Slope Stability
It is our understanding that the existing slopes up to 35 feet in height will remain.
Based on our experience and observation of the performance of similar smaller
slopes in the site area, it is our opinion that the existing 2 to 1 (horizontal to
vertical) slopes, will be grossly stable.
5.9 Concrete Flatwork
Concrete sidewalks and other flatwork (including construction joints) should be
designed by the project civil engineer and should have a minimum thickness of 4
inches. For all concrete flatwork, the upper 12 inches of subgrade soils should be
moisture conditioned to at least 3 to 6 percent above optimum moisture content
depending on the soil type and compacted to at least 90 percent relative
compaction based on ASTM Test Method 01557 prior to the concrete placement.
For all concrete flatwork driveways and sidewalks, the subgrade soils should be
should also be presoaked as discussed in Table 4 above prior to placement of
concrete, and should contain reinforcement steel with dowels into existing
adjacent concrete to the concrete placement. Moisture testing by Leighton should
be performed 24 hours prior to concrete placement.
5.10 Slope Maintenance Guidelines
It is the responsibility of the owner or owner's association to maintain the slopes,
including adequate planting, proper irrigation and maintenance, and repair of
faulty irrigation systems. To reduce the potential for erosion and slumping of
graded slopes, all slopes should be planted with ground cover, shrubs, and
plants that develop dense, deep root structures and require minimal irrigation.
Slope planting should be carried out as soon as practical upon completion of
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grading. Surface-water runoff and standing water at the top-of-slopes should be
avoided. Oversteepening of slopes should also be avoided during construction
activities and landscaping. Maintenance of proper drainage, undertaking of
improvements in accordance with sound engineering practices, and proper
maintenance of vegetation, including regular slope irrigation, should be
performed. Slope irrigation sprinklers should be adjusted to provide maximum
uniform coverage with minimal of water usage and overlap. Overwatering and
consequent runoff and ground saturation should be avoided. If automatic
sprinklers systems are installed, their use must be adjusted to account for rainfall
conditions.
Trenches excavated on a slope face for any purpose should be properly
backfilled and compacted in order to obtain a minimum of 90 percent relative
compaction, in accordance with ASTM Test Method 01557. Observation/testing
by the geotechnical consultant during trench backfill are recommended. A rodent-
control program should be established and maintained. Prior to planting, recently
graded slopes should be temporarily protected against erosion resulting from
rainfall, by the implementing slope protection measures such as polymer
covering, jute mesh, etc.
5.11 Landscaping and Post-Construction
Landscaping and post-construction practices carried out by the owner and their
representatives exert significant influences on the integrity of structures founded
on expansive soils. Improper landscaping and post-construction practices, which
are beyond the control of the geotechnical engineer, are frequently the primary
cause of distress to these structures. Recommendations for proper landscaping
and post-construction practices are provided in the following paragraphs within this
section. Adhering to these recommendations will help in minimizing distress due to
expansive soils, and in ensuring that such effects are limited to cosmetic damages,
without compromising the overall integrity of structures.
Initial landscaping should be done on all sides adjacent to the foundation of a
structure or associated improvements, and adequate measures should be taken to
ensure drainage of water away from the foundation or improvement. If larger,
shade providing trees are desired, such trees should be planted away from
structures or improvements (at a minimum distance equal to half the mature height
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of the tree) in order to prevent penetration of the tree roots beneath the foundation
of the structure or improvement.
Locating planters adjacent to buildings or structures should be avoided as much as
possible. If planters are utilized in these locations, they should be properly
designed so as to prevent fluctuations in the moisture content of the subgrade
soils. Planting areas at grade should be provided with appropriate positive
drainage. Wherever possible, exposed soil areas should be above paved grades.
Planters should not be depressed below adjacent paved grades unless provisions
for drainage, such as catch basins and drains, are made. Adequate drainage
gradients, devices, and curbing should be provided to prevent runoff from adjacent
pavement or walks into planting areas.
Watering should be done in a uniform, systematic manner as equally as possible
on all sides of the foundation, to keep the soil moist. Irrigation methods should
promote uniformity of moisture in planters and beneath adjacent concrete flatwork.
Overwatering and underwatering of landscape areas must be avoided. Areas of
soil that do not have ground cover may require more moisture, as they are more
susceptible to evaporation. Pending or trapping of water in localized areas
adjacent to the foundations can cause differential moisture levels in subsurface
soils and, therefore, should not be allowed. Trees located within a distance of 20
feet of foundations would require more water in periods of extreme drought, and in
some cases, a root injection system may be required to maintain moisture
equilibrium. During extreme hot and dry periods, close observations should be
carried out around foundations to ensure that adequate watering is being
undertaken to prevent soil from separating or pulling back from the foundation.
5.12 Future Investigation
The findings of this report indicate that the proposed grading is geotechnically
feasible. Prior to construction, additional geotechnical investigation will be
required to further evaluate metavolcanic rock and fill areas to provide additional
subsurface information regarding oversized rock and excavation characteristics
of metavolcanic rock. In addition, laboratory testing to assess soil corrosivity will
need to be performed during a future site investigation. This information may
then be utilized to provide additional construction level recommendations.
-29-
Lei~htcP
042631-001
5.13 Construction Observation and Testing and Plan Review
The geotechnical consultant should perform construction observation and testing
during the fine, and post grading operations, future excavations and foundation
or retaining wall construction at the site. Additionally, footing excavations should
be observed and moisture determination tests of the slab subgrade soils should
be performed by the geotechnical consultant prior to the pouring of concrete.
Foundation design plans should also be reviewed by the geotechnical consultant
prior to excavations.
-30-
042631-001
6.0 LIMITATIONS
The conclusions and recommendations presented in this report are based in part upon
data that were obtained from a limited number of observations, site visits, excavations,
samples, and tests. Such information is by necessity incomplete. The nature of many
sites is such that differing geotechnical or geological conditions can occur within small
distances and under varying climatic conditions. Changes in subsurface conditions can
and do occur over time. Therefore, the findings, conclusions, and recommendations
presented in this report can be relied upon only if Leighton has the opportunity to
observe the subsurface conditions during grading and construction of the project, in
order to confirm that our preliminary findings are representative for the site.
-31-
FIGURES
0
Feet
Project: 042631-001
Scale: 1 • = 2,000 '
Base Map: ESRI Resocrce Conte<, 2010
Themeuc Info: leighton
Author leighton Geometlcs (mmurphy)
Mep S.ved •• p \drlftit'lg\042e31\001\GIS'Iof_2012.00-21\Ftgurel.nu..d on G/2512012 4;30 40 PM
SITE LOCATION MAP
La Costa Town Center
Carlsbad, California
Lctghton
PLATE
A
...
~
I ...
-
210
;---'
Jsp
- - -APPROXJ"'-'TE C£Ol.OCIC CON'TACT
COWW:TED ru J'ROW ptt£V~DUS CAADINC (SCS.T. 2012)
;K, At 0 --OOSllNC fl.l
PlATE 2 CROSS-SECTION A-A'
LA COSTA. TOWN CfNTlilt c:NOLSIW> c.ouFOAHIA
APPENDIX A
REFERENCES
042631-001
APPENDIX A
REFERENCES
Blake, 2000, EQFAUL T, Version 3.0.
Bryant, W.A., and Hart E.W., 2007, Special Publication 42, Fault Rupture Hazard Zones
in California, Alquist-Priolo Earthquake Fault Zoning Act with Index to
Earthquake Fault Zone Maps, Interim Revision 2007.
California Building Standards Commission (CBSC), 2010, California Building Code
(CBC).
Hart and Bryant, E.W., 2007, Fault-Rupture Hazard Zones in California, Alquist-Priolo
Earthquake Fault Zoning with Index to Special Study Zones Maps:
Department of Conservation, Division of Mines and Geology, Special
Publication 42.
Jennings, C.W., 1994, Fault Activity Map of California and Adjacent Areas; California
Division of Mines and Geology, Geologic Data Map 6, Scale 1:750,000.
Kennedy, M.P., 1977, Geology of San Diego Metropolitan Area, California: California
Division of Mines and Geology, Bulletin 200.
Latitude 33 Planning and Engineering, 2012, Preliminary Site Grading Plan, La Costa
Town Center, Carlsbad, California, received September 2012.
Lindvall, S.C., and Rockwell, T.K., 1995, Holocene Activity of the Rose Canyon Fault
Zone in San Diego, California: Journal of Geophysical Research, V. 100,
No. B12, p. 24, 124-24, 132.
Southern California Soil & Testing, Inc., 2012, Update Geotechnical Investigation, La
Costa Town Square, North Residential Development, Carlsbad California,
dated January 3, 2012
Treiman, J.A., 1984, The Rose Canyon Fault Zone: A Review and Analysis, California
Division of Mines and Geology, Funded by Federal Management Agency
Cooperative Agreement EMF-83-K-0148.
A-1
042631-001
APPENDIX A (Continued)
---, 1993, The Rose Canyon Fault Zone, Southern California: California Division of
Mines and Geology, Open-File Report 93-2, 45p.
A-2
~----------------
APPENDIXB
LABORATORY TESTING
AND
FIELD DENSITY TESTS BY OTHERS
042631-001
APPENDIXB
Laboratory Testing Procedures and Test Results
Moisture and Density Determination Tests: Moisture content and dry density
determinations were performed on relatively undisturbed samples obtained from the test
borings. The results of these tests are presented in the boring logs. Where applicable,
only moisture content was determined from "undisturbed" or disturbed samples.
B-1
JOB NAME:
TEST
NO. DATE
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
1116104
1116104
1116104
1116104
1/16104
1116104
1116104
1119/04
1119/04
1119104
1119/04
1119104
1/19/04
1/19104
1/19104
1120104
1/20104
1/20104
1120/04
1128/04
1128104
1126104
1/29/04
1/29/04
1129/04
1129/04
1/29/04
1129/04
1/29104
1129/04
1/29/04
1130/04
1130/04
1130/04
1130/04
1/30/04
1130104
1130/04
215/04
215104
215104
2!5/04
215/04
215/04
2/5/04
2/12/04
2112104
2/12/04
2112104
La Costa Town Center
GRADING
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LOCATION
JOB NUMBER: 0411014-4
IN-PLACE DENSITY TESTS
ELEVATION MOISTURE DRY DENSITY SOIL REL.COMP.
(feet,MSL) (percent) (p.c.f.) TYPE (percent)
310.0
312.0
3140
3160
318 0
320.0
322.0
3240
326.0
328.0
3300
332.0
334.0
336.0
338.0
340.0
340.0
342.0
3420
358.0
361.0
369.0
344.0
344.0
346.0
346.0
348.0
3480
3500
350.0
352.0
352.0
354.0
354.0
356.0
356.0
358 0
3580
351.0
3530
3560
360.0
360.0
362.0
362.0
364.0
364.0
3660
3660
11.9
10.7
12.2
9.8
11.7
11.3
11.1
13.2
11.8
12.7
14.1
14.6
14.0
13.8
15.1
10.7
11.4
117
10.9
9.7
10.4
11.5
10.7
11.4
9.2
87
11.6
12.8
15.2
11.1
10.6
9.7
8.4
10.8
11.2
10.4
9.6
10.1
10.7
11.5
9.4
9.7
10.1
8.7
9.4
18.9
22.1
20.4
19.8
125.6
130.2
127.4
124.9
128.4
130.0
129.2
128.8
126.1
127.2
125.8
130 6
131.4
127.7
128.3
126.8
130.4
125.9
128.6
123.1
125.2
124.3
126.9
128.4
1302
125.6
127.7
127.4
125.2
130.0
126.8
125.4
130.6
129.9
127.4
1266
131.2.
126.3
129.6
130.1
12.5.9
126.7
125.4
128.2
127.3
100.7
100.4
100.£
100.9
IC
1F
10
1F
1E 2'F-
2E
2E
2F
2F
1E
IF
2F
2C
2E
1E
1F
10
1F
2A
28
28
IE
lF
1F
1D
1E
1E
10
1F
IE
1E
IF
1F
1F
1F
1F
IF
1F
1F
10
1E
IE
IF
1F
7
7
7
7
95.9
95.5
95.1
91.8
956
93.5
94.2
93.9
91.1
91.4
937
95.7
945
95.3
93.5
94.4
95.6
94.9
94.3
94.0
94.5
93.8
94.5
94.1
95.5
94.7
95.1
94.9
94.4
95.3
94.4
93.4
95.7
95.2
93.4
92.8
96.2
92.6
95.0
95.4
949
94.3
93.4
94.0
933
97.0
967
96.5
972
PLATE NO.3
JOB NAME:
TEST
NO.
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
86
89
90
91
92
93
94
95
96
97
98
99
100
DATE
2/13/04
2/13104
2/13/04
2/13/04
2117104
2/17/04
2117/04
2/17/04
2/17/04
2125/04
2/25/04
2125104
2125104
2125104
2125104
2/25104
2/25/04
2125/04
2125/04
2/25104
3/1104
3/1104
311!04
311/04
3/1/04
3/1104
3/1/04
3/1/04
311/04
3/1/04
3/1/04
3!2104
312104
3/2/04
312/04
312104
312/04
312104
3!2104
313104
313104
313/04
3/3/04
313/04
313104
318/04
3/12104
3/12104
3/12104
3112104
3/12104
La Costa Town Center
LOCATION
See Plan
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RETEST OF 63
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RETEST OF 74
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RETEST OF 76
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RETEST OF 85
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IN-PLACE DENSITY TESTS
ELEVATION MOISTURE
(feet,MSL) (percent)
364.0 10.6
364.0 11.1
366.0 9.6
366.0 9.2
366 0 17.9
370.0 18.1
372.0 16.9
374.0 20.4
3760 19.7
378.0 15.9
378.0 16.8
3800 14.6
380.0 13.8
372.0
371.0
372 0
371.0
374 0
3680
371 0
374.0
374.0
3730
3760
3780
378.0
374.0
374.0
374.0
3765
376.0
3785
3800
376.0
375.0
378.0
378.0
377.0
3800
380.0
3790
379.0
381.0
381.0
382.0
372.0
370.0
372.0
374.0
382.0 FG
381.0 FG
18.4
196
16.9
19.2
18.7
168
14.4
18.9
19.4
20.1
17.8
16.9
19.4
14.6
15.9
17.7
14.8
16.7
17.4
17.9
20.6
16.8
19.4
16.5
20.2
15.9
19.6
18.8
20.4
21.1
16.9
16.4
16.6
16.1
15.9
17.2
15.6
14.7
JOB NUMBER:
DRY DENSITY SOIL
(p.c.f.) TYPE
126.7 1E
130.2 1F
128.4 1E
131.2 1F
1094 3
110 1 3
109.2 3
106.9 4
107.3 4
107.9 4
106.8 4
107.8 4
109.1 4
89.7
94.8
93.9
95.2
99.6
108.2
109.8
97.7
101.1
95.8
97.9
92.1
94.6
99.2
104.6
102.9
101.6
100.9
101.5
100.7
102.4
101.1
99.4
100.9
101.6
102.7
103.6
101.9
102.7
100.9
104.2
100.8
102.9
102.0
101.6
104.7
103.1
102.0
7
7
7
7
7
4
4
7
7
7
7
7
7
5
5
5
5
5
5
7
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
0411014-4
REL.COMP.
(percent)
94.3
95.5
95.6
96.2
90.8
91.4
90.6
90.6
90.9
91.4
90.5
91.4
92.5
86.4
91.3
90.5
91.7
96.0
91.7
931
94.1
97.4
923
94.3
887
91.1
88.6
93.4
91.9
90.7
90.1
90.6
970
91.4
90.3
888
90.1
907
91.7
92.5
91.0
91.7
90.1
93.0
90.0
91.9
91.1
90.7
935
92 1
911
PLATE NO.4